Near field communications is a wireless connectivity technology which allows a communication over a short distance, for example 10 cm, between electronic devices, such as for example contactless smartcards or mobile telephones emulated in card mode, and readers.
NFC technology is particularly well adapted for connecting any type of user device and enables quick and easy communications.
A contactless object is an object capable of exchanging information via an antenna with another contactless object, for example a reader, according to a contactless communications protocol.
An NFC object, which is a contactless object, is an object compatible with NFC technology.
NFC technology is an open technology platform standardized in the ISO/IEC 18092 standard and ISO/IEC 21481 standard but incorporates several previously-existing standards such as for example the type A and type B protocols defined in the ISO-14443 standard, which can be communications protocols usable in NFC technology.
Aside from its conventional function as a telephone, a cellular mobile telephone may be used (if it is equipped with specific means) for exchanging information with another contactless device, for example a contactless reader, using a contactless communications protocol usable in NFC technology.
This allows information to be exchanged between the contactless reader and secure elements situated within the mobile telephone. Numerous applications are thus possible such as mobile ticketing for public transport (the mobile telephone behaves as a travel ticket) or else mobile payment (the mobile telephone behaves as a payment card).
Furthermore, Europay Mastercard Visa, abbreviated by the acronym EMV, is an international security standard for payment cards of the smartcard type initiated by the EMVCo consortium. The majority, or even the entirety, of bank smartcards conform to the EMV standard as do the majority, or even all, of the electronic payment terminal installations. The various publications encompassing the specifications of the EMV standard, in particular version 2.3 of November 2011, are available from the EMVCo consortium.
Furthermore, specifications, entitled “EMV Contactless Specifications for Payment Systems” and, in version 2.1 of March 2011 available from the EMVCo consortium, comprising four volumes, notably relate to the contactless communications protocol used for carrying out bank transactions between two contactless devices, and conforming to the EMV standard. The communications protocol for the EMV contactless standard is thus mainly based on the protocol described in the ISO/IEC 14443 standard.
When information is transmitted between a reader and an object emulated in tag or card mode, the reader generates a magnetic field by means of its antenna which is generally, in the standards conventionally used, a sinusoidal wave at 13.56 MHz having an amplitude in the range between 0.5 and 7.5 amps/meter.
On the other side, the antenna of the object emulating the tag modulates the field generated by the reader.
This modulation is carried out by modifying the load connected to the terminals of the antenna of the object.
By modifying the load across the terminals of the antenna of the object, the output impedance of the antenna of the reader changes owing to the magnetic coupling between the two antennae. This results in a change in the amplitudes of the voltages and currents present on the antennae of the reader and of the object. Accordingly, in this way, the information to be transmitted from the object to the reader is transmitted by load modulation to the antenna current of the reader. A copy of this current is generated and injected into the receiver chain of the reader where it is demodulated and processed in such a manner as to extract the information transmitted.
However, such a load modulation has certain drawbacks.
Indeed, the variation in load carried out during the load modulation results in a modulation in amplitude and phase of the signal (voltage or current) on the antenna of the reader.
The frequency spectrum of this signal comprises a main spectral line, centered for example at 13.56 MHz, which corresponds to the carrier (13.56 MHz), and two side lines corresponding to the useful signal containing the information transmitted by the object.
However, it turns out that the characteristics of these side lines present on the antenna of the reader can vary depending on the antenna designs and on the matching of their network, and on the position of the object relative to the reader.
The current readers only contain an amplitude demodulator for demodulating the signal (voltage) on the terminals of the antenna. For this reason, only the information on amplitude of the side lines is detected but not the phase rotation of the latter. However, in some situations, in other words when the phase modulation is preponderant with respect to the amplitude modulation, the rotation of the side lines may be close to around 90° then leading to levels of these side lines close to 0. So, in this case, the amplitude demodulator of the reader cannot detect the signals contained in these lines whose levels fall below its detection threshold (sensitivity threshold).
The result of this is then that such reader/object pairs cannot meet standards that require a correct functionality within a certain operating volume as is the case for the EMVCo standard. Indeed, there is a loss of communication in certain positions of the operating volume defined in these standards.
Quite clearly, by changing the position of the object in the operating volume with respect to the reader, the level of the amplitude modulation may then be increased with respect to that of the phase modulation so as to reestablish the communication. However, this is not a satisfactory solution.
Another solution would consist in incorporating into the reader not only an amplitude demodulator but also a phase demodulator. Unfortunately, such a modification is not possible in the current readers which contain only an amplitude demodulator.